Investigating the effect of capsular thickness and material properties on biomechanical and optical parameters in eye models

The mechanism of accommodation, which defines the shape change of the eye lens in order to provide clear focus over a range of distances, is still not fully understood. The uncertainties in understanding pose an obstacle to comprehending the causal factors in age-related loss of accommodation and in how to design effective accommodating implants to replace lenses with opacification caused by cataract. Finite element modelling has been widely used to study accommodation and can investigate parts of the lens, its capsule and anatomical entities involved in accommodation that are obscured by the iris in the living eye. This study investigated how the capsular thickness and the material properties of the lens affect the changes in the mechanical and optical properties of the lens during accommodation. Four lens models based on human lenses aged 16, 35, 40, and 48 years were constructed with capsules of different thicknesses and two types of material properties. The results show that the choice of material properties has a great influence on the lens shape change from both optical and biomechanical findings. The influence of the capsular thickness, and whether or not the capsule is modelled as having a constant or a variable thickness, also has an influence on the results of simulated shape change and this is most evident in the stress distributions. The significance of the findings are relevant to modelling studies that investigate accommodative function and to designers seeking to develop an accommodating implant.